Because i dont change that much in my products i dont face this problem very much, but after setting up new features for some products i also faced this neverending spinning buttons(save and stay/save).
I modified admin/themes/default/template/controllers/products/helpers/uploader/ajax.tpl as described above, and the spinning buttons indeed dissapeared, however 1 error still stays:

plugin.min.js:1 Uncaught ReferenceError: file_not_found is not defined
at plugin.min.js:1

For cvs import, I use always the (Sub)Category ID, I have setup a spreadsheet that convert the destination (sub)category to the ID category where the products belongs to.
Example:
ID name
43 Blouse
45 Panty
50 Long
50 Long sleeve
and so on.

When you have data from your supplier, with the follow: cat: blouse, sub: long, you use the sub cat to give it the right ID nr. When the sub. category are empty, I point to the Category to set the destination category. If the supplier Category are not your choice, you can give it easy the destination category ID, set it in you spreadsheet with the right destination ID (ID 60 define to my own category name).